This invention relates to a shaft seal assembly employed in a rotary machine, and in particular, to an assembly wherein the force developed by a high pressure sealing fluid is employed to radially center the seal assembly with respect to the shaft of the rotary machine.
In many high speed, high pressure machine applications, as for example those encountered in the turbine and compressor arts, the rotary components of the machine are mounted upon a shaft and the shaft is journaled for rotation within an opening formed in the end wall of a pressurized casing. Shaft seals are typically positioned within the shaft opening to prevent pressurized fluid from escaping to low pressure regions, as for example the atmosphere. In many applications, high pressure fluid is used in combination with mechanical seals to provide an effective seal system. The high pressure fluid is generally injected into a region at a pressure slightly above the pressure of the working fluid. In one form of seal system, the high pressure seal fluid generally flows from the injection region in opposite directions along the shaft, respectively toward a low pressure region or atmosphere, and toward the interior region of the machine containing the high pressure working fluid. A preponderance of the sealing fluid will flow toward the low pressure region at the exterior of the shaft opening. Typically, one or more pressure breakdown bushings will be provided about the shaft between the seal injection region and shaft opening to throttle, or breakdown, the pressure of the sealing fluid.
A seal ring is also disposed between the seal injection zone and the interior of the machine containing the working fluid. The sealing fluid will move inwardly between the opposed surfaces of the shaft and seal ring to develop a fluid barrier to prevent the working fluid from escaping from the rotary machine.
The shaft seals are generally mounted within stationary components of the rotary machine, with the opposed surfaces of the seals and components being in spaced apart relation. If a seal becomes grounded with respect to a stationary component, the seal responds as a journal with respect to the shaft and shares the shaft load with the machine's bearing system. This condition can have a deleterious affect upon the operation of the machine and the operating life span of the seals.